A parasite is a living organism that depends on a so-called host for food. It can live on this host, or within it.
Ectoparasites are also called external parasites. Many are haematophagous : they feed on the blood of the host by biting it like :
Others feed on skin or hair debris (keratin to be precise) such as Demodex or Sarcoptes scabiei, a mite responsible for scabies.
Some parasites live specifically in the ears of our dogs and cats. Notoedres cati is responsible for the famous cat scabies, or Otodectes cynotis.
Ectoparasites live on the host either permanently (as in the case of lice and scabies) or only during one phase of their life cycle. Mosquitoes, for example, only come to the host for a meal.
When we speak of internal parasites, we generally think of those that colonise the digestive tract. There are many of them and they are classified into roundworms, nematodes, and flatworms, cestodes. What is generally less well known is that some parasites can lodge in the respiratory tract like Aelurostrongylus abstrus in cats, or even in the bloodstream. This is the case for Babesia canis canis, which lives specifically in the dog’s red blood cells and is responsible for piroplasmosis, or Leishmania infantum, which lives for part of its cycle in the dog’s macrophages, a type of white blood cell, and is responsible for leishmaniasis.
Many parasitic infections of our four-legged friends are zoonoses. This means that these parasites can infect you too.
You have probably already heard of toxoplasmosis (Toxoplasma gondii), which is particularly dreaded by non-immune pregnant women, and which can be transmitted via raw meat or vegetables, or via cat faeces.
Toxocara canis is probably the most common source of intestinal infestation in young children. Parasite eggs ingested after contact with soil contaminated by the faeces of carrier dogs or cats. Sandboxes represent a major risk of exposure.
Echinococcosis, which is well known to people who like to go for walks in the forest, frequently affects foxes but can also infect dogs and cats and be transmitted to humans. Echinococcus is responsible, and there are two forms in our regions (E. granulosus and E. multilocularis).
Other examples are fleas, which can occasionally (if they have nothing else to eat) bite humans. As for lice, they are rather specific: dog lice only feed on dogs, cat lice only feed on cats, and human lice only feed on humans.
However, don’t panic, good hygiene (washing your hands after changing your cat’s litter or picking up your dog’s faeces, and before going to the table) as well as deworming and external antiparasitic protocols in line with your four-legged friend’s lifestyle can limit the risks of contamination. Talk to your vet.
Some parasites (referred to as intermediate hosts, HI) can transmit other disease agents by infesting or biting the final host (HD). For example, fleas (HI) can transmit Dipilydium caninum, a digestive worm, to our dogs and cats (HD). Ticks can also play this role by transmitting Borrelia burgdorferi, the bacterium responsible for Lyme disease, and Babesia canis; sandflies can carry Leishmania infantum or Dirofilaria immitis.
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